System for additively manufacturing composite structure

ABSTRACT

An additive manufacturing system is disclosed for use in fabricating a structure. The additive manufacturing system may include a support, and a print head configured to wet a continuous reinforcement with a liquid matrix and discharge the wetted continuous reinforcement. The print head may be operatively connected to and moveable by the support during discharge. The additive manufacturing system may also include a matrix control mechanism configured to selectively adjust an amount of matrix on the continuous reinforcement being discharged from the print head.

RELATED APPLICATION

This application is based on and claims the benefit of priority from U.S. Provisional Application No. 62/853,610 that was filed on May 28, 2019, the contents of which are expressly incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to a manufacturing system and, more particularly, to a system for additively manufacturing composite structures.

BACKGROUND

Continuous fiber 3D printing (a.k.a., CF3D®) involves the use of continuous fibers embedded within a matrix discharging from a moveable print head. The matrix can be a traditional thermoplastic, a powdered metal, a liquid resin (e.g., a UV curable and/or two-part resin), or a combination of any of these and other known matrixes. Upon exiting the print head, a head-mounted cure enhancer (e.g., a UV light, an ultrasonic emitter, a heat source, a catalyst supply, etc.) is activated to initiate and/or complete curing of the matrix. This curing occurs almost immediately, allowing for unsupported structures to be fabricated in free space. When fibers, particularly continuous fibers, are embedded within the structure, a strength of the structure may be multiplied beyond the matrix-dependent strength. An example of this technology is disclosed in U.S. Pat. No. 9,511,543 that issued to Tyler on Dec. 6, 2016 (“the '543 patent”).

Although CF3D® provides for increased strength, compared to manufacturing processes that do not utilize continuous fiber reinforcement, improvements can be made to the structure and/or operation of existing systems. For example, Applicant has found that greater control over an amount of the matrix wetting the reinforcement can improve properties (e.g., strength, stiffness, weight, etc.) of the resulting structure. The disclosed additive manufacturing system is uniquely configured to provide these improvements and/or to address other issues of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to an additive manufacturing system. The additive manufacturing system may include a support, and a print head configured to wet a continuous reinforcement with a liquid matrix and discharge the wetted continuous reinforcement. The print head may be operatively connected to and moveable by the support during discharge. The additive manufacturing system may also include a matrix control mechanism configured to selectively adjust an amount of matrix on the continuous reinforcement being discharged from the print head.

In another aspect, the present disclosure is directed to a method of additively manufacturing a structure. The method may include wetting a continuous reinforcement with a liquid matrix inside of a print head, and discharging the wetted continuous reinforcement through an outlet of the print head. The method may also include moving the print head during discharging, and selectively adjusting an amount of matrix on the continuous reinforcement being discharged from the print head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed additive manufacturing system; and

FIGS. 2 and 3, are isometric, diagrammatic of exemplary disclosed portions of the system of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system 10, which may be used to manufacture a composite structure 12 having any desired shape. System 10 may include a support 14 and a deposition head (“head”) 16. Head 16 may be coupled to and moved by support 14. In the disclosed embodiment of FIG. 1, support 14 is a robotic arm capable of moving head 16 in multiple directions during fabrication of structure 12. Support 14 may alternatively embody a gantry (e.g., an overhead-bridge or single-post gantry) or a hybrid gantry/arm also capable of moving head 16 in multiple directions during fabrication of structure 12. Although support 14 is shown as being capable of 6-axis movements, it is contemplated that support 14 may be capable of moving head 16 in a different manner (e.g., along and/or around a greater or lesser number of axes). In some embodiments, a drive may mechanically couple head 16 to support 14, and include components that cooperate to move portions of and/or supply power or materials to head 16.

Head 16 may be configured to receive or otherwise contain a matrix (shown as M). The matrix may include any types or combinations of materials (e.g., a liquid resin, such as a zero-volatile organic compound resin, a powdered metal, etc.) that are curable. Exemplary resins include thermosets, single- or multi-part epoxy resins, polyester resins, cationic epoxies, acrylated epoxies, urethanes, esters, thermoplastics, photopolymers, polyepoxides, thiols, alkenes, thiol-enes, and more. In one embodiment, the matrix inside head 16 may be pressurized (e.g., positively and/or negatively), for example by an external device (e.g., by an extruder, a pump, etc.—not shown) that is fluidly connected to head 16 via a corresponding conduit (not shown). In another embodiment, however, the pressure may be generated completely inside of head 16 by a similar type of device. In yet other embodiments, the matrix may be gravity-fed into and/or through head 16. For example, the matrix may be fed into head 16, and pushed or pulled out of head 16 along with one or more continuous reinforcements (shown as R). In some instances, the matrix inside head 16 may need to be kept cool and/or dark in order to inhibit premature curing or otherwise obtain a desired rate of curing after discharge. In other instances, the matrix may need to be kept warm and/or illuminated for similar reasons. In either situation, head 16 may be specially configured (e.g., insulated, temperature-controlled, shielded, etc.) to provide for these needs.

The matrix may be used to at least partially coat any number of continuous reinforcements (e.g., separate fibers, tows, rovings, socks, and/or sheets of continuous material) and, together with the reinforcements, make up a portion (e.g., a wall) of composite structure 12. The reinforcements may be stored within or otherwise passed through head 16. When multiple reinforcements are simultaneously used, the reinforcements may be of the same material composition and have the same sizing and cross-sectional shape (e.g., circular, square, rectangular, etc.), or a different material composition with different sizing and/or cross-sectional shapes. The reinforcements may include, for example, carbon fibers, vegetable fibers, wood fibers, mineral fibers, glass fibers, plastic fibers, metallic fibers, optical fibers (e.g., tubes), etc. It should be noted that the term “reinforcement” is meant to encompass both structural and non-structural (e.g., functional) types of continuous materials that are at least partially encased in the matrix discharging from head 16.

The reinforcements may be at least partially coated with the matrix while the reinforcements are inside head 16, while the reinforcements are being passed to head 16, and/or while the reinforcements are discharging from head 16. The matrix, dry (e.g., unimpregnated) reinforcements, and/or reinforcements that are already exposed to the matrix (e.g., pre-impregnated reinforcements) may be transported into head 16 in any manner apparent to one skilled in the art. In some embodiments, a filler material (e.g., chopped fibers, nano particles or tubes, etc.) and/or additives (e.g., thermal initiators, UV initiators, etc.) may be mixed with the matrix before and/or after the matrix coats the continuous reinforcements.

One or more cure enhancers (e.g., a UV light, an ultrasonic emitter, a laser, a heater, a catalyst dispenser, etc.) 18 may be mounted proximate (e.g., within, on, and/or adjacent) head 16 and configured to enhance a cure rate and/or quality of the matrix as it is discharged from head 16. Cure enhancer 18 may be controlled to selectively expose portions of structure 12 to energy (e.g., UV light, electromagnetic radiation, vibrations, heat, a chemical catalyst, etc.) during material discharge and the formation of structure 12. The energy may trigger a chemical reaction to occur within the matrix, increase a rate of the chemical reaction, sinter the matrix, harden the matrix, solidify the matrix, polymerize the matrix, or otherwise cause the matrix to cure as it discharges from head 16. The amount of energy produced by cure enhancer 18 may be sufficient to cure the matrix before structure 12 axially grows more than a predetermined length away from head 16. In one embodiment, structure 12 is at least partially (e.g., completely) cured before the axial growth length becomes equal to an external diameter of the matrix-coated reinforcement.

The matrix and/or reinforcement may be discharged together from head 16 via any number of different modes of operation. In a first example mode of operation, the matrix and/or reinforcement are extruded (e.g., pushed under pressure and/or mechanical force) from head 16 as head 16 is moved by support 14 to create features of structure 12. In a second example mode of operation, at least the reinforcement is pulled from head 16, such that a tensile stress is created in the reinforcement during discharge. In this second mode of operation, the matrix may cling to the reinforcement and thereby also be pulled from head 16 along with the reinforcement, and/or the matrix may be discharged from head 16 under pressure along with the pulled reinforcement. In the second mode of operation, where the reinforcement is being pulled from head 16, the resulting tension in the reinforcement may increase a strength of structure 12 (e.g., by aligning the reinforcements, inhibiting buckling, equally loading the reinforcements, etc.) after curing of the matrix, while also allowing for a greater length of unsupported structure 12 to have a straighter trajectory. That is, the tension in the reinforcement remaining after curing of the matrix may act against the force of gravity (e.g., directly and/or indirectly by creating moments that oppose gravity) to provide support for structure 12.

The reinforcement may be pulled from head 16 as a result of head 16 being moved by support 14 away from an anchor point (e.g., a print bed, an existing surface of structure 12, a fixture, etc.) 20. For example, at the start of structure formation, a length of matrix-impregnated reinforcement may be pulled and/or pushed from head 16, deposited against anchor point 20, and at least partially cured, such that the discharged material adheres (or is otherwise coupled) to the anchor point. Thereafter, head 16 may be moved away from anchor point 20, and the relative movement may cause the reinforcement to be pulled from head 16. As will be explained in more detail below, the movement of reinforcement through head 16 may be selectively assisted via one or more internal feed mechanisms, if desired. However, the discharge rate of reinforcement from head 16 may primarily be the result of relative movement between head 16 and anchor point 20, such that tension is created within the reinforcement. As discussed above, anchor point 20 could be moved away from head 16 instead of or in addition to head 16 being moved away from anchor point 20.

Head 16 may include, among other things, an outlet 26 and a matrix reservoir 24 located upstream of outlet 26. In one example, outlet 26 is a single-channel outlet configured to discharge composite material having a generally circular, tubular, or rectangular cross-section. The configuration of head 16, however, may allow outlet 26 to be swapped out for another outlet that discharges multiple channels of composite material having the same or different shapes (e.g., a flat or sheet-like cross-section, a multi-track cross-section, etc.). Fibers, tubes, and/or other reinforcements may pass through matrix reservoir 24 (e.g., through one or more internal wetting mechanisms located inside of reservoir 24) and be wetted (e.g., at least partially coated, encased, and/or fully saturated) with matrix prior to discharge.

Outlet 26 may take different forms. In one example, a guide or nozzle may located downstream of matrix reservoir 24, and a compactor (e.g., a wheel, a shoe, a wiper, etc.) may trail the nozzle (e.g., relative to a normal travel direction of head 16 during material discharge) and function to compact the material discharging from the nozzle. It is contemplated that either of the nozzle or the compactor may function as a tool center point (TCP) of head 16, to affix the matrix-wetted reinforcement(s) at a desired location prior to and/or during curing when exposed to energy by cure enhancer(s) 18. It is also contemplated that the nozzle may omitted, in some embodiments, and outlet 26 may simply include the compactor located at a discharge opening of any associated wetting mechanism(s).

One or more controllers 22 may be provided and communicatively coupled with support 14 and head 16. Each controller 22 may embody a single processor or multiple processors that are programmed and/or otherwise configured to control an operation of system 10. Controller 22 may include one or more general or special purpose processors or microprocessors. Controller 22 may further include or be associated with a memory for storing data such as, for example, design limits, performance characteristics, operational instructions, tool paths, and corresponding parameters of each component of system 10. Various other known circuits may be associated with controller 22, including power supply circuitry, signal-conditioning circuitry, solenoid driver circuitry, communication circuitry, and other appropriate circuitry. Moreover, controller 22 may be capable of communicating with other components of system 10 via wired and/or wireless transmission.

One or more maps may be stored within the memory of controller 22 and used during fabrication of structure 12. Each of these maps may include a collection of data in the form of lookup tables, graphs, and/or equations. In the disclosed embodiment, the maps may be used by controller 22 to determine movements of head 16 required to produce desired geometry (e.g., size, shape, material composition, performance parameters, and/or contour) of structure 12, and to regulate operation of cure enhancer(s) 18 and/or other related components in coordination with the movements.

It may be important, in some applications, to control an amount of matrix wetting the reinforcement. For example, some application may require a particular matrix-to-reinforcement ratio. In another example, a greater amount of matrix may be required at a particular location (e.g., along a particular side) of the reinforcement than at another side. FIGS. 2 and 3 illustrate ways to control (e.g., limit and/or steer) the amount of matrix clinging to the reinforcement.

One way to control an amount of matrix wetting the reinforcement is associated with controlling a tilt angle of outlet 26 relative to a trajectory of the reinforcement passing therethrough (e.g., an upstream and/or downstream trajectory). For example, it has been determined that a tilt angle α of outlet 26 relative to the trajectory of the reinforcement (represented by an arrow 98) can be selectively adjusted to effect at least one of (e.g., both of) a total amount of matrix being discharged and a location of the matrix relative on the reinforcement. As shown in FIGS. 2 and 3, the closer that the tilt angle α of outlet 26 is to the discharge direction (e.g., as α approaches zero), the greater the amount of matrix may be discharged together with the reinforcement. The reduction of matrix associated with a greater tilt angle α may be caused by a lip 100 at a distal end of outlet 26 pressing against the matrix-wetted reinforcement with a greater pressure. This pressure forces some of the matrix away (e.g., scrapes and/or pushes the matrix away) from the reinforcement at the engagement location. The forced-away matrix may move through the reinforcement towards an opposing side and/or up into outlet 26. In addition, the closer that the tilt angle α of outlet 26 is to the discharge direction, the more equally dispersed the matrix may be around the reinforcement. For example, as outlet 26 is tilted away from the discharge direction, only an inside portion of the reinforcement may be scrapped by lip 100, thereby generating an unequal distribution of the resin (e.g., the portion of the reinforcement engaging lip 100 may have less matrix than an opposite side of the reinforcement). In some embodiments, the tilt angle may be regulated to additionally control wetting of the interior of the reinforcement (e.g., by pushing matrix from the outside of the reinforcement towards the center).

The tilt angle of outlet 26 may be regulated by controller 22 via support 14 (referring to FIG. 1). For example, head 16 may be tilted by support 14 relative to structure 12, such that outlet 26 is placed at a desired angle α corresponding to a desired amount and/or distribution of the matrix. Controller 22 may selectively command tilting of support 14 based on a desired amount and/or distribution of matrix at a particular location (e.g., distance along the reinforcement and/or coordinates on structure 12). This command may be determined, at least in part, by referencing the particular location with one or more desired ratios and/or corresponding angles stored in memory.

FIG. 2 illustrates an additional matrix control mechanism 102 that may be used to regulate the amount of matrix allowed to cling to the outside of the reinforcement. It is contemplated that mechanism 102 may be used as an exit of matrix reservoir 24 and/or an entrance of outlet 26, as desired. It is also contemplated that mechanism 102 may be used together with active tilt-control of outlet 26 or alone, if desired.

Mechanism 102 may include, among other things, a compliant valve 104 that at least partially (e.g., completely) surrounds the reinforcement passing through head 16, and an actuator 106 that functions to selectively deform valve 104. In the disclosed embodiment, actuator 106 includes a threaded male base 108 located at one side of valve 104, a threaded female cap 110 located at an opposing side of valve 104, and a motor 112 that is operatively connected to one of base 108 and cap 110. In response to a command from controller 22, motor 112 may cause the connected base 108 and/or cap 110 to rotate (e.g., and thread together by a greater amount) and move axially closer together, thereby compressing compliant valve 104. This compression may cause valve 104 to deform radially inward and reduce an open cross-sectional area through which the reinforcement may pass. In this manner, an amount of restriction placed on the reinforcement (and thereby the amount of matrix allowed to remain on the reinforcement) may be actively controlled.

In one example, valve 104 has a generally conical shape and a tip of the conical shape pinches down on the reinforcement during rotation of base 108 and/or cap 110. It is contemplated that a flexible tube (not shown) could pass through the valve 104 and function as a guide for the reinforcement, if desired. In this embodiment, inward deformation of valve 104 may result in pinching of the tube and subsequently pinching of the reinforcement. It is also contemplated that valve 104 could have a shape other than conical (e.g., frustoconical, cylindrical, etc.), which may facilitate a more gradual application of pressure (e.g., less of a point-pinch).

It is contemplated that in addition to or in place of actuator 106, a pneumatic and/or hydraulic bladder could be used (e.g., around and/or inside of resilient valve 104) to variably restrict passage of the reinforcement through mechanism 102. For example, the bladder could be selectively filled with a pressurized medium, causing restriction to occur.

INDUSTRIAL APPLICABILITY

The disclosed system may be used to manufacture composite structures having any desired cross-sectional shape and length. The composite structures may include any number of different fibers of the same or different types and of the same or different diameters, and any number of different matrixes of the same or different makeup. Operation of system 10 will now be described in detail.

At a start of a manufacturing event, information regarding a desired structure 12 may be loaded into system 10 (e.g., into controller 22 that is responsible for regulating operations of support 14 and/or head 16). This information may include, among other things, a size (e.g., diameter, wall thickness, length, etc.), a contour (e.g., a trajectories, surface normal, etc.), surface features (e.g., ridge size, location, thickness, length; flange size, location, thickness, length; etc.), connection geometry (e.g., locations and sizes of couplings, tees, splices, etc.), reinforcement selection, matrix selection, desired matrix ratios and/or distributions, discharge locations, severing locations, curing specifications, compaction specifications, etc. It should be noted that this information may alternatively or additionally be loaded into system 10 at different times and/or continuously during the manufacturing event, if desired. Based on the component information, one or more different reinforcements and/or matrix materials may be installed and/or continuously supplied into system 10.

To install the reinforcements, individual fibers, tows, and/or ribbons may be passed through matrix reservoir 24 and outlet 26 (e.g., through features of the nozzle, and under the compactor). In some embodiments, the reinforcements may also need to be connected to a pulling machine (not shown) and/or to a mounting fixture (e.g., to the anchor point). Installation of the matrix material may include filling head 16 (e.g., reservoir 24) and/or coupling of an extruder (not shown) to head 16.

The component information may then be used to control operation of system 10. For example, the in-situ wetted reinforcements may be pulled and/or pushed from outlet 26 of head 16 as support 14 selectively moves (e.g., based on known kinematics of support 14 and/or known geometry of structure 12), such that the resulting structure 12 is fabricated as desired.

Operating parameters of support 14, cure enhancer(s) 18, matrix control mechanism 103, and/or other components of system 10 may be adjusted in real time during material discharge to provide for desired bonding, strength, tension, geometry, and other characteristics of structure 12. Once structure 12 has grown to a desired length, structure 12 may be severed from system 10.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. 

What is claimed is: 1 . An additive manufacturing system, comprising: a support; a print head configured to wet a continuous reinforcement with a liquid matrix and discharge the wetted continuous reinforcement, the print head being operatively connected to and moveable by the support during discharge; and a matrix control mechanism configured to selectively adjust an amount of matrix on the continuous reinforcement being discharged from the print head.
 2. The additive manufacturing system of claim 1, wherein the matrix control mechanism is disposed at least partially around the wetted continuous reinforcement at a location inside of the print head.
 3. The additive manufacturing system of claim 2, wherein: the matrix control mechanism includes a compliant valve having an opening through which the wetted continuous reinforcement passes; and an area of the opening is adjustable.
 4. The additive manufacturing system of claim 3, wherein the compliant valve further includes an actuator configured to deform the compliant valve and cause the opening to close.
 5. The additive manufacturing system of claim 4, wherein the actuator includes: a base located at a first side of the compliant valve; a cap located at a second side of the compliant valve and configured to engage the base; and a motor configured to adjust engagement of the cap with the base.
 6. The additive manufacturing system of claim 2, further including a controller in communication with the support and the matrix control mechanism, the controller being programmed to selectively cause the support to tilt the print head relative to a trajectory of the wetted continuous reinforcement through the print head based on a desired amount of matrix on the continuous reinforcement at discharge.
 7. The additive manufacturing system of claim 6, wherein the desired amount is a desired ratio of matrix-to-continuous reinforcement.
 8. The additive manufacturing system of claim 6, wherein the desired amount is a distribution of the liquid matrix on the continuous reinforcement.
 9. The additive manufacturing system of claim 6, wherein: the print head includes an outlet through which the wetted continuous reinforcement finally passes during discharge; and tilting of the print head causes a lip of the outlet to at least one of push matrix from a first side of the continuous reinforcement towards a second side of the continuous reinforcement and scrape matrix away from the continuous reinforcement.
 10. The additive manufacturing system of claim 1, wherein the matrix control mechanism includes a controller in communication with the support and programmed to selectively cause the support to tilt the print head relative to a trajectory of the wetted continuous reinforcement through the print head based on a desired amount of matrix on the continuous reinforcement at discharge.
 11. The additive manufacturing system of claim 10, wherein the desired amount is a desired ratio of matrix-to-continuous reinforcement.
 12. The additive manufacturing system of claim 10, wherein the desired amount is a distribution of the liquid matrix on the continuous reinforcement.
 13. The additive manufacturing system of claim 10, wherein: the print head includes an outlet through which the wetted continuous reinforcement finally passes during discharge; and tilting of the print head causes a lip of the outlet to at least one of push matrix from a first side of the continuous reinforcement towards a second side of the continuous reinforcement and scrape matrix away from the continuous reinforcement.
 14. A method of fabricating a composite structure, comprising: wetting a continuous reinforcement with a liquid matrix inside of a print head; discharging the wetted continuous reinforcement through an outlet of the print head; moving the print head during discharging; and selectively adjusting an amount of matrix on the continuous reinforcement being discharged from the print head.
 15. The method of claim 14, wherein selectively adjusting the amount of matrix includes adjusting an opening area of the outlet.
 16. The method of claim 15, wherein adjusting an opening area includes deforming a compliant valve located around the continuous reinforcement.
 17. The method of claim 14, wherein selectively adjusting the amount of matrix includes tilting the print head relative to a trajectory of the wetted continuous reinforcement through the print head.
 18. The method of claim 14, wherein selectively adjusting the amount of matrix includes selectively adjusting the amount of matrix based on a desired amount of matrix on the continuous reinforcement at discharge.
 19. The method of claim 18, wherein the desired amount is a desired ratio of matrix-to-continuous reinforcement.
 20. The method of claim 18, wherein the desired amount is a distribution of the liquid matrix on the continuous reinforcement. 